A large fraction of yield losses in wafer fabrication or processing of semiconductor devices is attributed to microcontamination. Contaminants can be organic or inorganic particles, films or molecular compounds, ionic materials, or atomic species. Examples of ionic contaminants are sodium, potassium, lithium, calcium, boron, manganese, sodium, titanium, zirconium, aluminum, sulfur and magnesium. Other damaging elemental impurities include heavy metals, for example, such as iron, copper, nickel, and gold.
The presence of contaminants during wafer processing has become particularly problematic in high density, large scale integration (LSI) technology. For example, contaminants can cause a device to fail by improperly defining patterns, creating unpredictable surface topography, inducing leakage currents though insulating layers, or accelerating device wearout.
Silicon wafers may be exposed to metallic or semimetallic contaminants during, for example, chemical mechanical planarization or polishing (CMP) or during other cleaning operations. CMP may, for example, involve holding or rotating a wafer of semiconductor material against a wetted polishing surface under controlled chemical fluid (i.e. slurry), pressure, and temperature conditions. The fluid typically consists of an abrasive component such as alumina or silica (unless it is utilized with a pad including an abrasive component) and a chemical etchant that chemically interacts with the surface. Generally, such fluid or slurries are quite pure; however, they are not free of contaminants such as the ionic contaminants listed above.
Chemical-mechanical planarization or polishing may be used to produce a surface with the desired end point or thickness. However, metal ions create contamination problems. For example, such contaminants may diffuse into the surface of the wafer and down fracture paths.
It has been reported that phosphonic acid chelating agents added to SC-1 wet cleaning solution (a mixture of NH.sub.4 OH, H.sub.2 O.sub.2, and H.sub.2 O) of an RCA clean commonly used to remove particles and organic contaminants on silicon surfaces, reduces certain metallic contamination deposition on a silicon wafer. This conclusion was reached in the article entitled "Thin-Oxide Dielectric Strength Improvement by Adding a Phosphonic Acid Chelating Agent into NH.sub.4 OH--H.sub.2 O.sub.2 Solution" by Akiya et al., J. Electrochem. Soc., Vol. 141, No. 10, October 1994. However, such wet cleaning procedures are performed after CMP processing and contamination may have already caused significant contamination problems to the wafer during the CMP process.
For the above reasons, improvements in the CMP process to reduce metal ion contamination of the wafer being processed are needed. The present invention as described below provides such improvements and overcomes the problems described above and those problems which will become apparent to one skilled in the art from the detailed description below.